JPH0118839B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a coated arc welding rod that successfully improves welding performance and welding workability by preventing stick burn of the coating material. Through adjustment, it is possible to prevent stick burn without adversely affecting hygroscopicity. [Prior Art] Today, welding is becoming more and more important as an indispensable joining method for all kinds of metal work, and is applied in various fields such as ships, bridges, vehicles, various mechanical products, and electrical products. There is. On the other hand, new welding methods such as carbon dioxide arc welding, electroslag welding, ultrasonic welding, and electron beam welding are being developed, but covered arc welding, which has been widely used in the past, can be used for a wide range of metal materials. It still accounts for the largest amount of consumption today because it is easy to use, can be applied anywhere, and has low equipment costs. By the way, when performing such covered arc welding, a covered arc welding rod (hereinafter also simply referred to as a welding rod) is heated by arc heat.
As a result, it was necessary to take into consideration the problem of so-called stick burn. When this stick burn occurs, (1) the arc becomes unstable during welding; Problems such as (2) disordered bead shape and (3) pits and blowholes occur, leading to a decline in welding workability and welding performance. Attempts have been made to address the above problems by changing the type and amount of water glass added to the coating, or by adding hydrated minerals such as talc, sericite, and bentonite to the coating. However, none of these countermeasures were sufficient to prevent stick burns, and therefore were not satisfactory in terms of welding performance and welding workability. [Problems to be Solved by the Invention] The present invention has been made in order to solve the above-mentioned problems, and it is possible to more reliably prevent stick burn in order to contribute to improving welding performance and welding workability. The purpose of the present invention is to provide a coated arc welding rod that can perform the following functions. [Means for Solving the Problems] The coated arc welding rod of the present invention that meets the above purpose is one in which the outer periphery of the core wire is coated with a coating material having a porosity of 10 to 25% as specified in the [Function] section. In particular, there is a gist. [Operation] Next, the structure and operation and effects of the present invention will be explained while tracing the research history that led to the completion of the present invention. The inventors added raw materials with high latent heat of melting and vaporization to the coating material based on the basic idea that the heat generated in the welding rod should be absorbed in some way to prevent stick burn. That's what I tried first. However, this method did not provide a satisfactory effect as a countermeasure against stick burn. Therefore, the inventors of the present invention did not take the position of ``absorbing the heat in the welding rod by using latent heat'' as mentioned above, but were wondering if there was an effective method to have it. The idea was to utilize the pores present in the agent and release the generated heat to the outside through the pores. Therefore, the next challenge is to understand how much of the above-mentioned pores should be included in the coating material, that is, what level of porosity should be set in order to prevent stick burn. Therefore, from now on, the explanation will mainly be about what level of porosity should be set in the coating material, but before that, the porosity measurement method used by the present inventors will be explained. FIG. 1 is an explanatory diagram of such a measuring method. First, (1) dry the coated arc welding rod at 110°C for 2 hours, and (2) measure the weight of the coated arc welding rod in this state (assuming the result is Ag). Next, (3) apply a resin coating to the coated arc welding rod using Kambi No. 250 (manufactured by Kansai Yushi Kogyo) diluted to 1/2 concentration with ethyl acetate, (4) dry it, and (5) After measuring the weight (the result is designated as Bg), (6) the weight is measured in water at 25°C to obtain the volume of the resin-coated coated arc welding rod (the result is designated as Cg).
Furthermore, (7) the core wire obtained by peeling off the coating material and coating agent from the welding rod is washed and dried, and then the weight of the core wire (8) is measured (result is Dg). To obtain the volume of the core wire, perform weight measurement in water at 25°C. (The result is Eg.) On the other hand, in order to measure the volume of water absorbed and adsorbed into the pores of the coating material, in addition to the measurement processes (1) to (9) above, the following process is performed to measure the volume of water absorbed and adsorbed into the pores of the coating material. Find the volume of water absorbed. That is, (10) immerse the dried coated arc welding rod in water at 25°C for 30 minutes, (11) take it out instantly, (12) wipe the excess moisture on the surface of the coating with a towel, and (13) weigh the rod. Perform measurement (result is Fg). The porosity is determined from the measurement results obtained in this way using the formula shown below. Porosity=(F-A)/ _ρ1 /(B-C)/ _ρ1- (
D-E) / ρ ₁ - (B-A) / ρ ₂ × 100 [%] [where ρ ₁ is the density of water at the measured water temperature (g/cm ³ )
, and ρ ₂ is the dry density (g/cm ³ ) of the coating resin. ] With this porosity measurement method, it is possible to measure pores of a certain size that are present in the coating material, but it is impossible to measure extremely microscopic pores. However, since macro to semi-macro pores having a certain size are effective as a countermeasure against stick burn, even if micro pores cannot be measured, the usefulness of this porosity measurement is not hindered. Now that we have finished explaining the porosity measuring method, we will now explain how much the porosity of the coating material should be. In general, the factors that determine the porosity of a coating material are (1) flux raw material composition and its ratio, (2) particle size distribution of the flux raw material, (3) content of water glass, (4) content of sodium alginate, (5) There are conditions such as kneading, painting, and drying conditions for the flux, but in the present invention, coated arc welding rods are prototyped using coating fluxes with various changes in the above-mentioned factors, and the porosity After measuring the porosity of the coating material using a measuring method and also measuring the hygroscopicity of the coating material, the coated arc welding rods were welded to examine whether stick burn occurred. The reason for measuring the hygroscopicity as well as the porosity is as follows. In other words, as the porosity increases, the hygroscopicity of the coating material also increases, but when a coating material with high hygroscopicity is used, a serious adverse effect appears on the hydrogen cracking of the weld metal, making it necessary to re-dry it before use. This is because there was a fear that the need arose, and especially in the case of low-hydrogen welding rods, the welding rods would not meet the moisture standards at all. Another drawback was that the number of pits and blowholes increased again as the amount of moisture absorbed increased. According to the above-mentioned study results regarding stick burn, in coated arc welding using a coating material with a porosity of 10% or less, (1) the bead shape becomes unstable;
It was found that (2) the coating became unstable, and (3) pits and blowholes were formed, causing problems due to stick burn. The reason for this problem is thought to be that when the coating material has a porosity of less than 10%, there are few escape routes for the generated heat, which causes the temperature of the coated arc welding rod to rise and cause stick burn. On the other hand, if the porosity is 10% or more, there is sufficient heat escape, so the above-mentioned problem does not occur, and stick burn is not inevitable. However, when the porosity exceeded 25%, the above-mentioned problem regarding hygroscopicity occurred. In other words, when the porosity exceeded 25%, a decrease in the strength of the weld metal and frequent occurrence of pits and blowholes were observed as described in the reason for measuring hygroscopicity. On the other hand, coating materials with a porosity of 25% or less do not cause the above-mentioned adverse effects due to hygroscopicity, and if covered arc welding is performed using a coated arc welding rod coated with a coating material with a porosity of 10 to 25%, It has been found that stick burn can be prevented as described above, and as a result, there are no practical problems in terms of welding performance and welding workability. [Examples] Example 1 A coating flux was prepared by adding water glass and sodium alginate to the flux raw materials shown in Table 1 and kneading them. This was coated on a 4 mmφ core wire and dried to obtain a coated arc welding rod.
The porosity was adjusted by variously changing the particle size structure of the flux raw material, the amount of water glass added, the amount of sodium alginate added, the drying conditions of the flux, etc.

[Table] Next, after measuring the porosity of the coated arc welding rod and investigating the hygroscopicity of the coating material, welding was performed under predetermined conditions and the status of stick burn was examined. These results are shown in Table 2.

【table】

[Table] Shown below.
○: 0.5%>, △: 0.5-0.7%, ×
:0.7%<
When stick burn occurs, defects in pit shape, instability of the arc, occurrence of pits and blowholes, etc. are observed in parallel, so in this example, stick burn was determined by paying particular attention to defective beat shape. . On the other hand, red heat on the stick occurs only when the stick is severely burnt. The various conditions in this example are as follows. Flux final drying conditions: 400°C x 60 minutes Welding conditions: 170 (A) Welding position: Downward moisture absorption conditions: 30°C x 80% x 4hr The results obtained from Table 2 are listed as follows. Test No. 1, 2, 3 with porosity of 10% or less
In this case, a normal beet shape could not be obtained and burnt spots occurred. In Test Nos. 4 to 11 in which the porosity was 10 to 25%, no stick burn was observed and the hygroscopicity of the flux was good. In test No. 12, where the porosity was 25% or more, no stick burn was observed, but the strength of the weld metal decreased due to increased hygroscopicity, and pits and blowholes occurred. Example 2 Example 1 was carried out using the flux raw materials shown in Table 3.
When we conducted a similar study, we obtained the results shown in Table 4. The various conditions in this example were as follows. Flux final drying conditions: 130℃ x 60 minutes Welding conditions: 170 (A) Welding position: Downward moisture absorption conditions (1) Flux C: 30℃ x 80% x 1hr (2) Flux D: 30℃ x 80% x 8hr The reason why the moisture absorption conditions of fluxes C and D are different is that the basic components of these fluxes are different.

【table】

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to provide a coated arc welding rod that can prevent stick burn and contribute to improving welding performance and welding workability.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing a method for measuring porosity in the present invention.

Claims (1)

[Claims] 1. Porosity determined by the following formula is 10 to 25%.
A coated arc welding rod characterized in that the outer periphery of the core wire is coated with a coating material. Porosity=(F-A)/ _ρ1 /(B-C)/ _ρ1- (
D-E) / ρ ₁ - (B-A) / ρ ₂ × 100 [%] [However, A: Dry weight of coated arc welding rod after drying at 110°C for 2 hours (g) B: Resin-coated coated arc welding Dry weight of rod (g) C: 25 of dried resin coated arc welding rod
Weight in water at ℃ (g) D: Dry weight (g) of the core wire after removing the resin coat and coating agent E: Weight of the core wire at 25℃ after removing the resin coat and coating agent
Weight in water (g) F: Weight (g) after immersing the coated arc welding rod in water at 25°C for 30 minutes and wiping off moisture on the coating surface ρ ₁ : Density of water at the measured water temperature (g/ cm ³ ) ρ ₂ :Dry density of coating resin (g/
^cm3 ). ]